Deville 4.6 gas mileage in winter?
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Cadillac DeVille 1985 to 2005 including:
1985-1992 Fleetwood, 1993 Sixty Special, All FWD Forum Discussion, Deville 4.6 gas mileage in winter? in Past Cadillac Vehicle Discussion; I was just wondering what kind of gas mileage people are gettin in their devilles in winter. My car lies ...
  1. #1
    03impala9c1's Avatar
    03impala9c1 is offline Cadillac Owners Member
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    Deville 4.6 gas mileage in winter?

    I was just wondering what kind of gas mileage people are gettin in their devilles in winter. My car lies to me saying i average 21 mpg in Wisconsin with 89 octane , though calculating it out I get more like 17. Cruising at 72 mph I get around 22-26 on a flat section of road which I know is horrible. I always use top tier gas, I'm debating if something is wrong with my car or are these cars are just that horrible in winter. During the summer months I averaged easily 7mpg better.

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    Submariner409's Avatar
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    Re: deville 4.6 gas mileage what are you getting in winter?

    Cold starts, cold oil - slower driving all take their toll. If your car is the base model or DHS you have a 3.11:1 final drive. In a Northstar in good tune that should give you an average of 12 - 16 city, 17 - 20 suburban/rural, 25 - 27 long term open road.

    As mileage piles up it takes the long term fuel average longer to catch up to true, current mileage. Remember - a half hour at 65 and 26 mpg plus a half hour of idling and 0 mpg = 13 mpg average for that hour.

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    Ranger's Avatar
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    Re: deville 4.6 gas mileage what are you getting in winter?

    I'm getting 22 around home. 26 on a 300 mile trip up north to Eagle River to go snowmobiling. I run 87 and have no allegiance to any brand.

    If you think yours may be low, check the FPR. A leaky FPR diaphragm will certainly lower your mileage.

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    rodnok01's Avatar
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    Re: deville 4.6 gas mileage what are you getting in winter?

    I get about 22 also, half rural half stop and go. On the highway 25+.
    I can tell you any lead footing drops my mileage considerably.

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    UM Rebel is offline Cadillac Owners Member
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    Re: deville 4.6 gas mileage what are you getting in winter?

    I get 26 - 27 on the highway and about 17 -20 around town. I try to run 100% gasoline when I can. We have a few stations here that sell it. I've never noticed winter making any difference, but I live in south Louisiana.

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    Slipgate is offline Cadillac Owners Enthusiast
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    Re: deville 4.6 gas mileage what are you getting in winter?

    I get around 21 overall in the summer and around 19 in the winter. I attribute it to the winter mix gas we have around here.

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    Re: deville 4.6 gas mileage what are you getting in winter?

    I get about 14-15 in town, and regularly clear 26 on the open road.

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    Re: deville 4.6 gas mileage what are you getting in winter?

    Doesn't sound too far off then. If im right the computer calculates mileage by the amount of fuel used. Last fillup I noticed it stated I used 11.5 gallons from last fillup but filling it up again it stopped at 13.7. Calculations between the two were considerably off. Id suggest you all try and compare the same as I to see is your vehicle calculated mpg is accurate. Im just floored on the difference between summer and winter when it comes to mpg with this car. All my driving is rural/interstate driving 70+ miles a day so its not in cold cycle very long comparing to engine runtime. Ive noticed acceleration mpg went from 11-13 in summer to 3-7 mpg instant in winter. My driving habits havent changed one bit so idk. And yes, my particular deville is a base and yes it does have the 3.11s. Im very knowledgeable about vehicles, gm in particular, I just dont know how factory sets up these northstars...

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    Re: deville 4.6 gas mileage what are you getting in winter?

    Correct. The PCM compares fuel used to miles driven. Fuel used is measured by counting injector pulses and pulse widths.

    I've never noticed more than 1-2 MPG decrease in winter.
    jounier11 and jounier11 like this.

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    Re: deville 4.6 gas mileage what are you getting in winter?

    I get like 10MPG still trying to figure out why lol

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    Re: deville 4.6 gas mileage what are you getting in winter?

    Quote Originally Posted by SGWORLDWIDE View Post
    I get like 10MPG still trying to figure out why lol
    Because you're 25 and your right foot is ten pounds heavier than your left.

  13. #12
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    Re: deville 4.6 gas mileage what are you getting in winter?

    Hell Im 52 and still have that extra weight in my right foot and here i thought it was all in my belly lol, but im getting anywhere from 15.7 to almost 20 1 time.. Ive only had my car for 2 months now but still....

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    The Donald is offline Cadillac Owners Fanatic
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    Re: deville 4.6 gas mileage what are you getting in winter?

    Quote Originally Posted by Ranger View Post
    I'm getting 22 around home. 26 on a 300 mile trip up north to Eagle River to go snowmobiling. I run 87 and have no allegiance to any brand.

    If you think yours may be low, check the FPR. A leaky FPR diaphragm will certainly lower your mileage.
    Whats FPR ??

  15. #14
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    Quote Originally Posted by The Donald View Post
    Whats FPR ??
    Fuel Presure Regulator

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    Re: deville 4.6 gas mileage what are you getting in winter?

    Fuel Pressure Regulator - as in the 'Acronyms' sticky post just above this one.

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